Sputtering apparatus is widely used for etching and deposition processes. Atoms are knocked out of the surface of a target and travel through the space of an evacuated chamber. A significant number of the ejected atoms eventually etch the target and are deposited on the surface of a substrate to coat it with target material.
In sputter deposition of material on a substrate the sputtering system parameters such as temperature of the target and substrate, utilization of target material and uniformity of deposition on the substrate are critical to acceptance of any commercial sputtering system. These parameters may be advantageously controlled by applying perpendicular electric and magnetic fields to the target by forming a magnetron system which traps electrons near the target surface to improve their ionizing effect. Such systems have been found to provide improved deposition rates and to reduce the heating of the substrate due to the impact of particles.
Sputtering systems using magnetron devices often use the target material inefficiently due to undesirable erosion patterns of the target which allow much of the target material to be unused although the target itself becomes unusable. One common erosion pattern experienced with planar type magnetrons for example is the well known race track erosion pattern in which an oval portion of the target surface is exhausted with the rest of the target surface fully intact and relatively unused.
The target material of magnetron systems during operation tends to be very hot due to large ion currents generated. Adequate cooling must therefore be provided to the magnetron device to assure its proper operation.
Similarly the trajectory of ionized particles must be controlled in order to prevent the generation of excess heat on the surface of the substrate being coated due to impact energy.
It is essential that all these requirements be achieved in a magnetron device that is cost effective if the device is to be commercially successful. Presently available magnetron devices tend to be very expensive to construct due to complicated construction arrangements requiring close dimensional tolerances and complicated servicing of cooling and electrical systems.
The three most common types of magnetron device geometry are the cylindrical, circular and planar type constructions. Circular and planar type constructions tend to suffer from localized erosion problems which render the target unusable even though useful material remains. Cylindrical magnetron devices are more uniform in their erosion but are expensive to construct and are not suitable to coat substrates with large planar surface areas. The cylindrical magnetrons may be inverted in that the inside surface of the cylinder is the target and the substrate is located within the cylinder. These magnetrons, sometimes designated hollow cathode magnetrons, advantageously simultaneously sputter both sides of a substrate and contain sputter action within a region defined by the interior of the hollow cathode. They require a hollow cylindrical target with target matrial being sputtered from an interior surface and typically use complex solenoid arrangements to generate the magnetic containment field. They are very expensive to fabricate.
Simultaneous sputtering of both sides of a substrate can also be accomplished by using two facing planar magnetrons in which the substrate passes between two planar magnetrons. This arrangement is not as efficient as the hollow cathode configuration and has all the erosion problems of the single planar magnetron.